Project Title: Tropospheric Scintillations
Project Description:
The phase of radio waves propagating through the earth's troposphere is
perturbed by irregularities in the refractive index. At microwave
frequencies, these perturbations are dominated by water vapor
fluctuations. Phase perturbations are important because they affect
the "seeing conditions" of imaging radio interferometers and because,
if uncalibrated, they may be the limiting noise source in future
searches for low-frequency gravitational radiation using Doppler
tracking of spacecraft.
This project involves the measurement of statistics of tropospheric
scintillations observed using using very-high-precision spacecraft
tracking data and, as appropriate, a cross-spectral analysis of radio
phase fluctuations with water vapor radiometer (WVR) data taken
simultaneously. In addition to second-moment statistics (power
spectra, structure functions), the magnitude and frequency of
occurrence of non-stationary tropospheric "events" are also of
interest.
Background Information:
The data were taken at three sites (California, Spain, Australia)
nearly continuously for 19 days and over a wide range of tropospheric
conditions. The data were "X-band" (~8.4 GHz), so the effect of phase
perturbations imposed by charged particles (e.g. the ionosphere) were
minimized. The data have been reduced to phase residuals. The phase
residuals have to be inspected and partitioned into regions that are
approximately statistically stationary and into regions of
non-statistical events. Spectral, cross-spectral, and structure
function analysis will be done, building the required programs from an
existing subroutine library.
Literature References:
On the relevance of phase scintillation to the low-frequency
gravitational wave search problem: Armstrong, J. W., Woo, R., and
Estabrook, F. B. 1979, Ap. J. 230, 580.
Existing observations of tropospheric phase fluctuations, e.g.:
Armstrong, J. W. and Sramek, R. A. 1982, Radio Science, 17, 1579;
Sramek, R. A. 1989, in "Radio Astronomical Seeing", J. E. Baldwin and
Wang Szhouguan, eds. (Pergamon: Oxford)
A general review of wave propagation in a random medium: Ishimaru, A,
"Wave Propagation and Scattering in Random Media" (Academic Press: New
York)
Requirements:
The sponsor requires that interested students meet the following
requirements: Junior or senior level standing with course work and
interest in applied mathematics (particularly numerical analysis and
linear algebra); possibly a mathematics major with some exposure to
computer science. Familiarity with FORTRAN, some exposure to
probability and its applications, and some exposure to a UNIX
environment are required.
This opportunity is for:
Caltech students. Will consider non-Caltech students
Research Sponsor
Sponsor: John Armstrong
Division: JPL
Mail Code: 238-737
Phone: (818) 354-3151
E-mail: john@oberon.jpl.nasa.gov